1. Field of the Invention
The invention is drawn to microbial compositions and their use for reducing the ammonium concentration of wastewater.
2. Description of the Prior Art
Municipal and agricultural waste disposal is a major problem. Agricultural animals such as swine and other livestock are commonly reared in facilities that are specially designed to manage manure and liquid waste generated by the animals. For example, in some swine rearing facilities, swine are raised in enclosed facilities that have slatted floors. Beneath the floors are pits for receiving swine manure and urine that pass through the slatted floor. These pits contain water that is occasionally drained to remove the livestock waste. Other facilities raise swine on a hard slanted floor, and periodically wash accumulated manure and urine from the slanted floor. Still other facilities use a combined approach, and have slatted floors on which the swine are raised, and a slanted floor underneath that is periodically washed to remove accumulated manure and urine. Water that is used to flush manure in these facilities is often pumped into large tanks that can be quickly discharged to rapidly flush manure from the facility. Dairy cows are also often raised in facilities that must periodically be washed of animal manure and urine. The dairy cows are often fed in a sheltered pen that has a hard concrete floor that is periodically washed.
The proper management of the wastewater collected from these livestock rearing facilities poses a significant challenge for the producer or farmer. Manure excreted by the livestock generate ammonia as well as hydrogen sulfide, methane, volatile fatty acids, phenols and other gases that contribute to the offensive odor in many livestock rearing facilities. Liquid manure generated from livestock production is a major contributor to ammonia emissions in rural areas (Arogo et al., 2001. Ammonia in animal production: A review. ASAE Paper No. 014089; De Visscher et al., 2002. Ammonia emissions from anaerobic swine lagoons: Model development. Journal of Applied Meteorology, 41, 426-433). These emissions may produce acidification and eutrophication of coastal waters, lakes, streams, and terrestrial ecosystems, resulting in habitat degradation and a reduction in biodiversity (Vitousek et al., 1997. Human alteration of the global nitrogen cycle: Causes and consequences. Issues in Ecology, 1, 1-17).
Historically, livestock producers and farmers have utilized a number of techniques for managing wastewater from livestock rearing facilities. Some have disposed of the wastewater directly upon fields, while many others have treated the liquid wastes in anaerobic holding ponds or lagoons before application onto the land.
In municipal and industrial systems, ammonia from wastewater can be removed by a variety of physicochemical and biological processes (Metcalf & Eddy, 2002. Wastewater Engineering: Treatment and Reuse. McGraw Hill, Boston, Mass.), but biological processes are preferred because they are usually more cost effective (USEPA, 1993. Nitrogen control. USEPA, Washington, D.C.). Biological removal of ammonia through the process of nitrification and denitrification is regarded as the most efficient and economically feasible method available for removal of nitrogen from wastewater (Tchobanoglous, G. and F. L. Burton, Wastewater Engineering Treatment, Disposal, and Reuse, Boston, Mass.: Irwin/McGraw-Hill, 1991): The effectiveness of the biological nitrogen removal process depends on the ability of nitrifying organisms (or ammonia oxidizing bacteria, AOB) to oxidize ammonium ions (NH4+) to nitrite (NO2−) and nitrate (NO3−). Subsequent reduction of molecular nitrogen, i.e., denitrification, may be essential as well if one desires to reduce total nitrogen as well as ammonia nitrogen. This later step is rapid with available carbonaceous substrate and an anaerobic environment, conditions which are typically found in farm settings in constructed wetlands or liquid manure storage units. However, the reaction rate of the nitrification is extremely low compared to that of denitrification, so that nitrification normally will be a rate limiting step in the biological nitrogen removal process (Vanotti and Hunt, 2000. Nitrification Treatment of Swine Wastewater with Acclimated Nitrifying Sludge Immobilized in Polymer Pellets. Transactions of the A.S.A.E., 43, 405-413).
Ammonia oxidizing bacteria, AOB, have been previously described, and consist of three genera, the marine-associated Nitrosococcus (γ-proteobacteria), and the terrestrial-associated Nitrosospira (β-proteobacteria) and Nitrosomonas (β-proteobacteria) (Head et al., 1993. The phylogeny of autotrophic ammonia-oxidizing bacteria as determined by analysis of 16S ribosomal RNA gene sequences. J Gen Microbiol, 139 Pt 6, 1147-53). The genus Nitrosomonas is divided into five lineages: N. communis; N. cryotolerans; N. europaea/eutropha; N. marina; and N. oligotropha (Koops and Pommerening-Roser, 2001. Distribution and ecophysiology of the nitrifying bacteria emphasizing cultured species. FEMS Microbiology Ecology, 37, 1-9); with N. europaea/eutropha lineage isolates being the most commonly isolated lineage from activated sludge (Wagner et al., 2002. Microbial community composition and function in wastewater treatment plants. Antonie Van Leeuwenhoek, 81, 665-80).
The implementation of ammonia removal technology in livestock effluents is particularly difficult in winter months. It has been previously documented that nitrification by AOB is dependent upon several environmental factors, the most critical being dissolved oxygen concentrations (Andersson and Rosen, 1990. Upgrading for biological nitrogen removal—Some full-scale experiences from Sweden. Water Science and Technology, 22, 93-104; Sharma and Ahlert, 1977. Nitrification and nitrogen removal. Water Research, 11, 897-925), pH (Andersson and Rosen, 1990. ibid; Shammas, 1986. Interactions of temperature, pH, and biomass on the nitrification process. Journal of the Water Pollution Control Federation, 58, 52-59), and temperature (Andersson and Rosen, 1990, ibid; Sharma and Ahlert, 1977, ibid; Wild Jr et al., 1971. Factors affecting nitrification kinetics. Journal of the Water Pollution Control Federation, 43, 1845-1854). In fact, the rate of nitrification by AOB is severely affected by temperature (Characklis and Gujer, 1979. Temperature dependency of microbial reactions. Prog. Wat. Tech., Suppl. 1, 111-130; Sharma and Ahlert, 1977. ibid; Wild Jr et al., 1971. ibid).
Knowles et al. demonstrated that AOB in particular are drastically affected by temperature changes (Knowles et al., 1965. Determination of Kinetic Constants for Nitrifying Bacteria in Mixed Culture, with the Aid of an Electronic Computer. J Gen Microbiol, 38, 263-78), and studies of various waste management systems employing nitrification have reported failure during winter temperatures (Ilies and Mavinic, 2001. The effect of decreased ambient temperature on the biological nitrification and denitrification of a high ammonia landfill leachate. Water Res, 35, 2065-72; Kim et al., 2006. Effect of temperature and free ammonia on nitrification and nitrite accumulation in landfill leachate and analysis of its nitrifying bacterial community by FISH. Bioresour Technol, 97, 459-68). Working with nitrification in activated sludge, Borchardt found an optimized activity between 15 and 35° C. and a sharp drop of nitrification rate at temperatures <15° C., with 50% reduction at 12° C. and 100% at 5° C. (Borchardt, 1966. Nitrification in the Activated Sludge Process The Activated Sludge Process in Sewage Treatment Theory and Application. Univ. of Michigan, Dept. of Civil Eng., Ann Arbor, Mich.). Similarly, Randall and Buth demonstrated that both nitrite and nitrate formation were strongly inhibited by temperatures of 10° C. or less (Randall and Buth, 1984. Nitrite build-up in activated sludge resulting from temperature effects. Journal of the Water Pollution Control Federation, 56, 1039-1044). According to Shammas, high nitrification efficiency can only be obtained with either very long detention time or a combination of high nitrifier concentration and elevated temperature (Shammas, 1986. ibid). Increased detention time means larger reactors and capital cost. For waste water treatment systems in areas which experience colder temperatures (<15° C.), nitrification activity rates can be addressed by inputting heat to the system and maintaining a stable temperature. This poses a problem for the low cost treatment of animal waste because the energy input required for heating such systems comes at a large economic expense.
Thus, while many improvements have been made in the removal of nitrogen from animal wastes in wastewater, the need remains for further improved techniques for reducing this nitrogen.